Ceramic blades for probing small pads in close proximity have been known and are in common use, however, due to inherent limitations the ability to reach frequencies above 2 gigahertz has not been achieved by prior art. Basically, this limitation is due to the geometry and method of attachment of the needle onto the blade and its physical orientation. Many types of blades have been employed in attempting to solve the problems of high frequency probing while allowing an acceptable contact force and compliance without distorting the signal with undue insertion or return loss. A search of the prior art did not disclose any patents that read directly on the claims of the instant invention, however, the following U.S. patents were considered related:
______________________________________ U.S. Pat. No. Inventor Issue Date ______________________________________ 3,560,907 Heller Feb. 2, 1971 4,161,692 Tarzwell Jul. 17, 1979 4,195,259 Reid et al Mar. 25, 1980 4,423,373 LeCroy, Jr. Dec. 27, 1983 ______________________________________
P. V. N. Heller teaches an arrangement whereby a plurality of individual flexing arms are apportioned in a circular array. The flexing arms are spring loaded to provide resiliency with wire leads connected on the outside periphery of the enclosure to terminal posts for transmitting the electrical signal. The contact point that is contiguous with the workpiece is integrally formed with the connector contact which engages a prescribed point in the circuit, thereby permitting the conducting of measuring circuit response by external equipment.
Tarzwell uses an "L" shaped ceramic support member having an elongated end with a thin metalized portion along the narrow edge surface to which a bent needle is attached by soldering. The needle is parallel to the ceramic member and curved downward. The tip of the needle is sanded flat to produce a surface parallel to the support member. In one embodiment, metalized portions are positioned parallel on the side of the support member to provide a power and signal path for the test equipment signal.
While a needle is attached to a metalized portion on the edge or the side of Tarzwell's invention, the needle is always parallel and bent downward near the tip. This is true of some commercially available probe blades that are in common use today and employ some of the features as taught by Tarzwell. An example of this type of probe blade is the series ACS manufactured by Wentworth Laboratories, Inc., or type 301 produced by Cerprobe of Tempe, Ariz.
Reid et al uses an "L" shaped extension arm that is adjustable in angular displacement with a support sleeve retaining a probe tip in the form of a needle with a downwardly depending end. A force sensitive material is attached to the arm of the probe detector device and is bordered by silver plated regions with wires soldered to the plates.
LeCroy, Jr. utilizes a test probe having two substantially rigid electrically conducting members which are insulated from each other. This probe embodiment is for background purposes as indicative of the art to which the invention relates.
It may be seen that overall system low frequency probing has been the main thrust of the above inventions and the art has approached the elevated frequency problem with little regard to minimize the insertion and return losses on the probes themself.